Currently, exploding foil initiators (EFI's) represent the “state of the art” with regard to devices for initiating detonation in an explosive charge through a relatively high-energy pulse or shockwave as exploding foil initiators are insensitive to induced or radiated electrical energy, such as electromagnetic interference (EMI) or low energy pulses, and utilize a secondary explosive, which are relatively impervious to impacts and high temperatures, for producing the high-energy pulse. The ability to withstand impacts as well as electrical, electromagnetic and thermal energy renders exploding foil initiators relatively safe and thus very desirable for a significant number of detonation applications. Consequently, exploding foil initiators are widely used in military applications, such as warhead fuzes as detailed in Military Standard Mil-Std-1316: Safety Criteria for Fuze Design. This standard provides guidance for initiation technologies that can be used in-line with a warhead main charge explosive train. The unique characteristics of an EFI allow it to meet the requirements for in-line useage without any interrupter or alignment mechanism. The safety of the design is shifted in large part to the electronic circuits that arm the firing circuit that initiates the EFI. This unique capability enables the EFI to be remotely located from the safety circuit, which further enables designs that can fire sequentially or with a high degree of simultaneity. These distributed designs require only one set of safe and arming circuits, minimizing the weight, volume and cost of the design.
Despite their success and relative safety in applications where detonation is desired, exploding foil initiators have not been widely used in pyrotechnic applications where deflagration rather than detonation is desired. One drawback with the use of exploding foil initiators in pyrotechnic applications concerns the strength of the shockwave that is typically produced; the shockwave produced is ordinarily so strong as to actually damage or detonate the pyrotechnic material, rather than to initiate its burning as desired for proper operation. Consequently, a bulkhead between the EFI and the pyrotechnic device is commonly employed to attenuate the shockwave and limit the amount of energy that is transmitted to the pyrotechnic material.
The use of the bulkhead of the pyrotechnic ignition system, however, is undesirable because of the added weight and volume. A further concern includes the need for expensive machining of the bulkhead to ensure accurate attenuation of the shockwave since the pyrotechnic material would fail to ignite if the shockwave were to be too severely attenuated. Conversely, if the shockwave is not sufficiently attenuated, there is a risk of damaging the pyrotechnic system and having a safety or reliability failure. The variation in the output of the initiator and effects of temperature on the materials further compound this problem and require costly quality controls to ensure the safety and reliability of the system. This requires qualification and acceptance testing of the assembly with system hardware and critical inspections of the bulkhead interface.
In view of the above noted drawbacks, low energy initiation systems are most commonly employed to initiate a deflagration event in a pyrotechnic material. Such low energy initiation systems typically include a bridge or hot wire that must be in very close proximity to a pyrotechnic initiation material. The close proximity of the bridge or hot wire to the pyrotechnic ignition material, however, increases the potential, relative to initiation systems that utilize exploding foil initiators, for inadvertent or accidental initiation as a result of EMI or lightning, for example. These hot wire devices are therefore required to be kept out of alignment with the pyrotechnic train and need to be moved into alignment prior to firing. This is accomplished by the use of electromechanical devices to translate or rotate the initiator and the pyrotechnic acceptor into alignment. These devices are inherently expensive, bulky and add significant weight. Further the device must be located next to the pyrotechnic compound being ignited provide adequate safety, reducing the design options and increasing design complexity.
In view of the aforementioned drawbacks associated with exploding foil initiators and low energy initiation systems, there remains a need in the art for an improved initiation device for initiating a deflagration event in a pyrotechnic material in a very reliable and safe manner.